The popular, English language derived name for occlusive epicutaneous testing is "patch test".
This term "patch test" reflects the fact that from the end of the 19th century onwards patches of fabric or paper were employed which were soaked with a test substance. The importance of occlusion for obtaining reliable and reproducible results became increasingly clear from the 1950's onwards. Various different types of patches have been brought forth with a view to obtaining occlusion and an adequate transfer of test substance to the skin: See for example U.S. Pat. No. 3,703,809, U.S. Pat. No. 3,894,531, U.S. Pat. No. 4,214,592, U.S. Pat. No. 4,158,359, U.S. Pat. No. 4,390,027, U.S. Pat. No. 4,450,844 and WO-A-86/01994. The term "patch" is construed in a very broad sense nowadays in the present context. In our specification and claims therefore the word "patch" designates the area carrying the test substance and applied to the skin. The most popular patches according to conventional technique are small cups of aluminum or plastic (Finn Chambers.RTM., Epicon Oy, Finland, and Chemotechnique Diagnostic AB, Malmo, Sweden, respectively) or small aluminum disks provided with filter paper (Al-test, Holister Stier, USA). On these conventional patches, the test substance formulated in a suitable vehicle has been applied immediately before the testing. The vehicle most commonly employed has been petrolatum (vaseline), but in the case of some, problematic contact allergens (e.g. formaldehyde) it was preferred to employ patches of fabric or filter paper soaked with the test substance dissolved in a suitable solvent (e.g. water). WO-A-86/01994 and Br. J. Dermatol. 112 (1985) pp 63-8 are considered to have come forward with an entirely new generation of patches.
The technique is called "TRUE Test"; it employs a patch which is a thin, dry polymer film capable of absorbing moisture from a tested skin area when the patch is applied under occlusion against the skin The most preferred vehicles have been said to be those that will then form a gel In a patch according to the TRUE Test method, a homogeneous distribution of the test substance in the polymeric film has been achieved already in the manufacturing stage The TRUE Test is the first system capable of providing customers with high-quality patches comprising a guaranteed quantity of test substance.
Occlusive epicutaneous testing for demonstrating contact allergy is performed with pressure-sensitive adhesive strips on which one or more patches containing a test substance have been applied Such strips may thus carry as many as up to 25 patches, although in most cases the number of patches is less than 15. It is known that the strips can be wrapped in materials that are impermeable to air, moisture and light.
In the epicutaneous testing procedure, an allergenic substance in the form of a suitable formulation is applied to normal skin under occlusion for a predetermined period of time and in a correct manner. This will then, in contact allergy cases, produce an allergic eczema in the test area. Irritant substances give rise to irritative eczema reactions of a similar character (Manual of Contact Dermatitis: Fregert S., 2nd edition, Munksgaard, Copenhagen (1981), pp 71-6). The side of the patch facing away from the skin is impermeable to moisture, to thus provide the said occlusion.
As far as we know, prefabricated formaldehyde patches for use according to the conventional patch test have never been available commercially. Fairly satisfactory patches for use in the TRUE Test for the purpose of demonstrating formaldehyde allergy could be constructed by means of having formaldehyde or paraformaldehyde in the form of a cyclodextrin complex incorporated in a polymeric film (EP-A-252,044). It has been found, however, that alternative solutions are needed for tackling the problems relating to formaldehyde.